ill ,t^ 

Iii5l7&5 



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lilfl 

llllll 

fililil 

liilltii 

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lii 

iilll 
mm 

Ill 

iill 

iii 
III 

liii 



lilif 

iili 

iliii! iili^i^l 




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■;;W,|lS,<;ii|ii; 

|si!|l|i|j|ijj| 




Class.. ^3JdJ-^i 



THE SALMON OF THE YUKON RIVER :::::: 
::::::::::::::: By Charles H. Gilbert 

From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXXVIII, 1921-22 
Document No. gzS : : : : : : : : : : : : : Issued November 21, 1^22 




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THE SALMON OF THE YUKON RIVER :::::: 
::::::::::::::: By Charles H. Gilbert 

From BULLETIN OF THE BUREAU OF FISHERIES, Volume XXXVIII, 1921-22 
Document A'o. g2S : : ; ; ; ; ; ; ; ; .- Issued Xovember 21, 1^2:^ 




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THE SALMON OF THE YUKON RIVER. 

By CllARI.i:S H. GlI.HKKT, 

Professor of Zoolotiy, Stanford University. 

CONTENTS. 

Piige. 

Introdiictii)n 317 

Tlic king salmon (Oiicorhynchiis tschmcylscha) 31S 

Rate of travel 318 

Growth and age at maturity 320 

The chum or dog salmon (Oncorhynchus kflo) 325 

Rate of travel 326 

Year classes 326 

Proportions of sexes. . 327 

Size at maturity - 328 

Growth and scale readings 329 

The sockcye salmon (Oncoihynchus nerka) 330 

The coho salmon (Oncorhynchus kisutch) 331 

The hum])back salmon (Oncorhynchns gorhuscha)- . 332 

INTRODUCTION. 

Tlie summer of 1920 was spent by tlie writer, in company with Henry O'lMalley, at 
that lime field assistant of tlie United States liureau of I'isherics, in investigating the rims 
of salmon to the Yukon River. The primary object of the expedition was to ascertain the 
advisability of permitting the operation of one or more salmon canneries on the Yukon, 
in view of the possibility that they might so curtail the salmon supply that it would fail 
to provide natives, and white inhabitants as well, with the stores of fish that they find 
essential under the rigorous conditions f)f the far northern climate. It was to be deter- 
mined whether there existed an excess above the needs of the inhabitants that could 
safely be used for commercial purposes for export beyond tlie boundaries of Alaska. 

This phase of the situation has been dealt with in a report to the Commissioner of 
Fisheries and was published in 1921.' Some of the details that are given in that report 
concerning the movements of the salmon during their run and the rate of travel that they 
maintain in their ascent of the river are herein repeated, but the body of the present 
paper is concerned with the growth-history of the Yukon salmon and the ages at which 
they have reached matiuity. The Yukon River is near the northern limit of range for 
the Pacific salmon. The effect of the arctic cold on growth and age of maturing is an 
interesting problem. 

'Investigation of the Salmon Fishcrit-s <it tlie Yukon River, by Charles H. Gilbert and Henry O'Malley, Iliireaii 01 
Fishfiies Document No. gooa, pp. n-.s-ij.}. WashingLon. rgsi. 

317 



3I« BULLETIN OF THE BUREAU OF FISHERIES. 

Three of the five species of salmon that occur along the Pacific shores of North 
America enter the Yukon Basin in sufficient numbers to constitute distinct runs. These 
are the king or chinook salmon, the chum or dog salmon, and the coho or silver salmon. 
The names here given are those by which these species are kno\\Ti in other districts of 
Alaska and generally along the coast to the southward. Unfortunately, in the Yukon 
Basin, there is confusion in this regard. The coho or silver salmon is most frequently 
called chinook, while the various grades of the chum or dog salmon are known as "silvers, ' ' 
"half-breeds," and "dogs." The king salmon alone, of the three species that ascend 
the river in numbers, is called by the same name by which it is elsewhere designated. 

The two remaining species of Pacific coast salmon, the humpback and the sockeye 
or red salmon, enter the river each year in small numbers and have no economic impor- 
tance. To what extent the individuals of these species may be strays from other streams 
that have well-defined runs has not been determined. 

The material on which the present paper is based was obtained from June 15 to 
July 31, 1920, at the cannery of the Carlisle Packing Co., located in the entrance to 
Kwiguk Channel, a branch of the Kwikluak or South Mouth of the Yukon. 

THE KING SALMON (Oncorhynchus tschawytscha) . 

The king salmon is the most highly prized for human consumption of the three 

Yukon species. It is also valued for dog feed, especially in the upper course of the river, 

for by the time the salmon have fought their way upstream a thousand mUes or more even 

the richest species contains no more oil than is needed to furnish satisfactory dog feed. 

As it enters the mouth of the river, the Yukon king is the richest salmon known to us. 

It there drips oil profusely when hung on the racks to dry and is, in fact, too rich for most 

successful canning. The canned product, if handled roughly, or if shipped to distant 

points, is ita danger of breaking down to a substance of mushlike consistency. King 

salmon taken at some point higher up the river, where a portion of the oil would have 

been expended during the ascent, would in this respect furnish a better commercial 

product. 

RATE OF TRAVEL. 

The nm begins at the mouth of the river in the latter part of May or early in J une, 
almost as soon as the river is clear of ice after the spring break-up ; and it lasts as a com- 
mercially valuable run for about three weeks. Tradition has it the king salmon appear at 
points as high as Tanana and the Ramparts at the same time as the first steamer that 
ascends the river from St. Michaels on the opening rif navigation. This would indicate 
an luiprecedentedly high rate of travel in a river with very swift current. Such incom- 
plete data as we have concerning the ascent of salmon in other rivers indicate a rate not 
to exceed 10 to 20 miles per day. But in the Yukon Basin the distances to be traversed 
are great — some of the spawning beds being 2,000 to 3,000 miles from the sea — -and the 
summer season is much shorter than in any other large salmon river. These two factors 
necessitate a high rate of speed in ascending the river, and the fact that this has been de- 
veloped in the Yukon salmon is one more instance of close adaptation to the conditions of 
their environment on the part of a highly localized race. Rapid ascent of a river means 
expenditure of energy out of all proportion to the distance to be traversed. Unusual 
stores of potential energy in the form of oil are therefore required by the Yukon salmon. 
We have already referred to the unusually rich provision of oil in the case of the king 



SALMON OF THE YUKON RIVER. 



319 



salmon, and the same is true of tlie chum or dog salmon of the Yukon, which excels in 
richness and amount of oil the chum salmon from all other rivers in as great a degree as 
that which distinguishes the Yukon kings from other king salmon. 

As regards the rate at which they ascend the river, we have more reliable and complete 
data for the Yukon than have been secured in any other stream. Records were obtained of 
their first a]jpearance at a large number of localities. Some of these were ascertained by 
means of wireless messages sent during the early days of the run, before the dates of the first 
captures should be forgotten. Many others were obtained during our ascent of the river in 
early August, when all fishing camps were visited and records were inspected concerning 
the run of the summer. In a number of instances complete written records were available, 
which gave not only the date on which Ihe first captures were made, but the numbers of 
fish taken on each day of the season. WHiile we recognize th;it the capture of the first 
salmon of the season at dilTerent points along tlie ii\er may vary within a few days in 
relation to the beginning of the run, we are convinced from an examination of our data 
that this source of error is not serious and that reliable conclusions concerning rate of 
travel can be drawn from the table (i) presented below. WTienevcr two or more records 
were obtained from different fishermen in the same locality tlie earliest has been selected. 

It will be noted that the lowest rates of travel apparently occur in the lower course of 
tlie river. But the results are here obscured by the known fact that salmon, on entering 
the tidal area of a stream, move back and forth with the tides for an undetermined period, 
before seriously undertaking the ascent of the river. The influence of this factor, how- 
ever, will not alone suffice to explain the constant increase in rate of travel as far up the 
river as Tanana, where it had reached an average for the entire river below this point of 
62 miles per day over a period of 1 3 days. 

Above Tanana, tlie rate again decreases, possibly due to the retarding influence of the 
Rampart Rapids together with the general increase in current found in the upper portion of 
tlie river, but the rate exhibits an unmistakable tendency again to augment as Dawson is 
approached. The first king salmon to reach Dawson in the middle of July, 1920, had 
been traveling against a consistently rapiil cuirent for 29 days, at the rate of 52 miles per 
day, and during this period, as always within the river, had taken no food. 



Table i. 



-DaTKS of CVPITRIC l)F I'IKsr Kl.NO S.M.MON AT A 

RjvER During Seaso.x 



■F l.nc \T,!Tli:S .VlONG TUE YuKO.N 



Locality 


Date. 


Approxi- 
mate 
number 
of miles 

traveled. 


Miles 
traveled 
per day. 


I^-ality. 


Date. 

Jimc 27 
...do 

June 2S 


Approxi- 

mate 
number 
ul miles 

traveled. 


Miles 
traveled 
per dai". 




June Is 
June 15 
June 20 






Whiskev Creek, above Louden . 

Ruby 

Tanana 


622 
659 

S04 

I. 117 
1,402 

1^478 
1,504 


w 










Pilot Station 

Marshall 


107 
144 
204 
259 
2:9 
346 
440 
491 
555 


2Q 

M 

40 


f>2 




June 21 
Jime 22 
June 23 
June 24 
June 27 
June 28 
June .'9 


Rapids July i 

Circle ': tulv ii 




Paimiiit 


•17 




Charlie Creek 

Kajile 

lie WoU's fii>h camp. 

Dawson 


July 12 
July 1,1 

J"iy 14 
,..do...- 




Halls Rapids, above Anvic. 
Camp SI miles below Kaltag . . . 
Kaltag 


50 
$1 











The season of 1920 was notably late in Alaska ; tlie break-up occurred in the Yukon 
fully a week later than usual, and the salmon were equally delayed in entering. As 
shown by the above table, the first king salmon taken in the delta was captured June 13. 



320 BULLETIN OF THE BUREAU OF FISHERIES. 

The run culminated quickly within a week after that date, then maintained itself at a 
fair level for about three weeks, and was practically over by the close of the first week 
in July. Stragglers appeared during subsequent weeks in July and August but became 
less and less numerous. 

GROWTH AND AGE AT MATURITY. 

We have no knowledge concerning the feeding grounds of the Yukon salmon and 
must leave the question open to what extent, if at all, the young traverse the passes in 
the Aleutian Chain and attain their growth in the North Pacific. It is entirelv possible 
that throughout their life in the ocean, they remain within the confines of the Bering 
Sea. None of them have been detected traversing the channels between the Aleutian 
Islands, nor have they been recognized elsewhere along lines of their migration routes 
in the sea. 

Conditions in Bering Sea, it would seem, must be less favorable for rapid growth than 
in districts farther south. The northern part of the sea and a strip around the coasts, in- 
cluding Bristol Bay, are covered with ice floe during the winter and early spring months. 
The temperatures to which the salmon are tlien exposed must be near the freezing 
point. At the time they seek the river nioutli in May or June the surface temperature 
in Bering Sea approaches 40° F. Under such adverse conditions growth during the 
winter season must be at or near a standstill and in the spring might well not be 
resumed before the beginning of the streamward migration. In that event tlie scales 
would exhibit no growth accomplished during the year in which the fish was captured. 
A salmon in its fifth year would indicate in its scale structure the completion of four 
full years' growth, and the margin of the scale would be formed by tlie wnter check of 
the fourth year. In other districts to the southward the salmon of the spawning run 
have already responded to spring conditions and have begun a period of rapid growth 
before entering the streams. The scales have participated in this renewed growth, 
and the margins exhibit a larger or smaller band of widely spaced rings, which lie out- 
side the winter check of the previous year. But in the case of the Yukon king salmon 
this is not present. The winter check of the previous year forms the margin, and 
usually no trace exists of any growth belonging to the cuixent year. A very few cases 
form doubtful exceptions to this genei-alization, with the outer one to three rings more 
widely separated at least in a portion of their course. This featiu-e is shown dis- 
tinctly in the accompanying series of photographs of tlie scales of Yukon king salmon, 
ranging from those in their third to those in their seventh year (Figs. 276 to 2S5). 

Another striking peculiarity of the Yukon king salmon is found in their early his- 
tory as fry and fingerlings. We did not secure any of the yoimg, although attempts 
were made to capture them with minnow seines on their downward migration, near the 
mouth of the river. But tlie central areas of the adult scales contain records of the 
early history and show conclusively in every instance that the young remained in 
fresh water for a full year's growth before descending to the sea. In the photographs 
that follow, the line "i" points to the outer margin of the stream growth, which 
presents a nucleus of finely crowded lines, beyond which are the \videly spaced lines 
indicating rapid growth after reaching the sea. 

This habit of the Yukon kings is in striking contrast to what is obser\^ed in streams 
farther south. In the Fraser River, the Columbia, the Klamath, the Sacramento, and 



SALMON OF THE YUKON RIVER. 32 1 

all other streams thus far examined a eonsiderable proportion of the adult salmon are 
developed from fry that passed to sea during their first year and com[)leted only a 
small portion of their first year's growth in fresh water. This "sea tyi)e" dcvelojis 
at an earlier age than do those that tarry a year in fresh water, and it frequently 
constitutes half or more than half the entire run. The absence of the "sea type'' in 
the Yukon may well be related to the severity of the fall and winter, the lateness of the 
sjiring, and the shortness of the summer season. It would seem that tiie hatching of 
the eggs, the absorption of the _\i>lk, and the emergence of the fry from the gravels 
must be corresjjondingly retarded. 

A third ijeculiarity of the \'uk<)n king salmon consists in the retardation of the 
age at which they attain maturity. In the Columbia River, where, owing to the use of 
beach seines, wheels, and tra])s, the smaller salmon arc captured in due juoportion 
with those of larger size, the youngest chinooks of stream tyjie that are captured in the 
sjjawning run are in their second year. These arc all male fish, as are those of the ne.\t 
larger size, which arc in their third year. T'emale chinooks of stream tvpe do not inatiu'c 
in the Columbia until their fourth \'ear, when they arc not far inferior in muiilx-rs to 
males of equal age. The commercially valuable portion of the Columl^ia Ri\er run con- 
sists of 4 and 5 year fish. Com[)aratively few individuals reach their si.Ktli year, and 
none has to my knowledge been re])orted in its seventh year. The condition in the 
Yukon is far dilTerent. Ko 2-year fish were secured, and but one 3-year fish, which 
was a male, 16 inches king, the scale of which is represented in Figure 276. 

In spite of the fact that fishing was prosecuted exclusively bv gill nets, whicli 
during tlie king salmon run were of large mesh (8i or Sj inches), fish of diminutive 
size were frequently entangled in the web and captured. Special attention was paid 
to the.se, witli tlie object of ascertaining the earliest age at which maturity would be 
attained in the Yukon race. In addition to the 16-inch individual in its third year, 
above noted, we examined 44 specimens ranging from 17 to 27 inches, all of them males, 
in tlieir fourth year. I-'rom this it is aj)parent that no female king saluKin mature on 
the Yukon until after their fourth year. They are therefore retarded at least one 
year in reaching maturit\', as compared Avith king salmon in the more southern part 
of the range of the species. (See Figs. 277 and 278.) 

Continuing the examination of larger sizes we encountered tlie first 5-year male 
at 25 inches, the males of this age ranging from 25 to 40 inches. In the fifth year, for 
Uie first time, we encountered female salmon, but these were very few in luimber. 
Among the 131 individuals in their fiftli year that we have examined, selected wholly 
by size witliout reference to sex, there are iig males and only 12 females. This indi- 
cates a still furtlier retardation in age of maturing of females. \ot only arc there no 
4-year mature females (so abundant in more temperate latitudes), but comparati\'ely 
few females develop maturity even at the age of 5. The 12 of which we have record 
lie in size within the range of the 5-year males, the smallest being 30 and the largest 37 
indies long. (See Figs. 279 and 280.) 

The male 6-year fish are numerous, the 79 individuals represented in our series 
ranging widely from 29 to 48 inches. There is thus a wide overlap in size between the 
5 and the 6 year fish, as is always the case, although, as will be noted, the 4 and the 5 
year males show but little overlap. Among the 6-year fish, for the first time, females 



322 



BULLETIN OK THE BUREAU OF FISHERIES. 



are really abundant, exceeding in number the males of equal age. Of the 185 6- year 
individuals, selected without reference to sex, 79 are males and 106 females. (See Figs. 
281 to 28.V) 

Another e\adence of retai'ded development is found in the class of 7-year fish. In 
streams thus far studied from, the vSacramento to the Fraser it is very rare for a king 
salmon lo attain the age of 7 years. Only two such specimens have been observed to 
my knowledge. In the Yukon, however, members of this class are not uncommon. 
Although not specially sought for, 42 are included in our series, 10 of these being males 
and 32 females. Here, again, the late development of females compared witli males 
is made evident. (See Figs. 284 and 285.) 

Table 2 gives the distribution by sex, age, and length of all the king salmon of our 
Yukon series of the run of 1920. For comparison similar data from a series taken from 
the run of 1919 by C. F. Townsend, fisheries inspector for the Bureau of Fisheries, are 
included in tliis table. It should be noted that the relative size of these various classes 
in our series does not represent their relative abimdance in the run. While no selec- 
tion was made by sex, frequent selection was made by size at critical points. Thus, 
special attention was paid to the smaller sizes, and these appear in our series in 
more than their normal proportions. The same is ti'uc of individuals approximating 
30 inches in length. It was at this size that females first were found, and individuals 
of this length were specially selected for examination. 

T.\BLK 2. — King S.\lmon rnoM Moith Yiko.n- River, 1920 and 1919, Distributi;d by Age and bv 

Length. 





Nunibcr of specimens, 1920. 


Number of specimens, 1919. 


LpQglb. 


4 
vears — 
Malcs.i 


S years. 


6 years. 


7 years. 


4 
^ears— 
Males.- 


S ycart. 


6 years. 


7 years. 




>'-'-' nS«. 


Males, 


Fe- 
males. 


>'■""■ miles. 


Males. 


Fe- 
males. 


Males. 


I'C- 

malcs. 


Males. 


Fe- 
males. 




I 
3 
4 
3 
3 
6 
10 
S 
.1 
4 


, 




i .. . 








, 










1 






, 


















^ 











( 












1 






















3 2 inches 
































I 
5 
5 
II 
10 

6 

2 















24 inches 





























I 






















27 inches 


s 






I 






















" 








;9 inches 




20 

1'^ ' 

II 3 
5 3 
JO 2 

9 

4 1 2 

1 1 I 
4I 

2 1 

H 




















?o inches 












I 













I 














j2 inches 














5 








s 












I 




^4 inches 1 . . . . 


5 3 
9 10 
3 10 
9 .S 
7 14 

s 13 

3 13 
7 S 

6 7 


1 


3! ' ■ 

I 1 T I 






;s inches ... 


3 


■■■■,0!;:::.:: 

4 ' 

5 1 








57 inches 1 


4 6 






2 i 






,... 








^Q inches 


;;;;;;; 





I , 








40 inches 




7 


\' 


I 


4.; inches 
























I 

I 


2 




























\ 


■, 












I 

X 








I 














I 












47 inches 













I 












t 


i 


1 y-'-- ■■■■■■■ 












Total 


44 


119 12 


79 


I oft 


10 


-,2 j 40 


16 ! 5 ! 20 1 35 1 7 1 S 


Average length in 
inches 


;.!■ 4 


31.3 ; 33-5 


3S. 7 


3S. 5 


41. 8 


1 

^0. I 1 26. ^i 


31 1 SJ.l. 1 37- S 36 


41.7 


}•-,■ 7 



' One ,^-year-iiId i()-inch male was discovered in i(>;o. No 4-year-old females were oh-ervcd. 
' No 4-year-old females were found. 



SALMON Ol' THE VVKOX KIVKR. 



The follnwiiij; laljle (.;) gives the average sizes attained by tlie dilTcreiil year classes 
in the two years kjiq and 1920, the males and females being stated separately. In 
comparing these with similar averages obtained in other districts, we must bear in mind 
that our Yukon material shows no growth belonging to the season in which the fish were 
captured. Our 4-year indi\-iduals had comi)leted three years of growth, but no more, 
and similarly v.-ith each of the other year groups. However, no strict comparison is 
possible between ^■ukon 4-year fish anfl the vycar fish from other localities, for although 
the latter had produced a certain amount of new growth in their third year, they had 
not eom]ilcted the growth of the tiiird year when they ceased feeduig and were caj)- 
fnrcd. In like manner no e.\act correspondence c;ui be expected between ,s-\ear 
\'ukon individuals p.nd 4-year material from the Columbia or the I'raser. In com- 
jxiring growth rates from these different U)calities, the most satisfactory basis will be 
found in com[)leted lengtiis of the different yeai' classes, computed from the .scales. 
Ijy length is meant the distance, measured over the curve of the body, from ti]) of snout 
to distal end of midtlle caudal rays. 
'r.\m.i; ;. — .\vi;K.\r,i; I,i;.n(;ths i'dr Cicrt.mn \'v..\k C.Kori's nv N'ikijn' Ki\<; S.\i mox. nj-'o .\n'i> 1019. 



t>cx an<l year. 



Males: 

1920. 

1919. 
Fcniuk-s; 

iq-o. 
1919. 



3-year group. 



4-year group. 



length, i 



.\veracc 
lenKth. 



J.1.4 
it- 3 



5-ycar croup. 



.\vcracc 



6-ycar Kroup. 



lengtl;. 






.(s-o ! 



-Average 
Icnyth, 



79 .'**• 



106 

IS 



36 



r-year group. 



Average 
Icngtli. 



41. .s 



For comparison with other regions we have calculated the growth for each year of 
their lives of 77 fish belonging to the fourth, fifth, sixth, ;uid seventh year classes and 
present the results in Tablc4. We have followetl I'raser's latest ])aper- in taking 1 .5 inches 
(40 mm.) as the average length of the fry when the first scale ring was formed. Several 
differences are encountered in comparing our results with Fraser's. His material was 
largely taken in the Gulf of Georgia and included a mixture of fish that would mature 
during the then current sea.son with others that would delay maturing for one or more 
years; also, doubtless, a mi.xture of races, bound for different river basins and unlike in 
certain of their characteristics. His measurements are throughout smaller than by our 
method, inasmuch as they do not include the length of the middle caudal ra3's. 

Table 4, which follows, shows with regard tf) each year class that the growth durijig 
the year that precedes maturity is greater than during the corresponding year of classes 
that reach a greater age. Thus the third year's growth of fish that mature in their fourth 
year is greater than the third year's growth in fish that would not mature luilil their liftli, 
sixth, or .seventh years. Furthermore, it is greater in 5 than in 6 year fish and greater 
in individuals that mature in their sixth than in those that mature in their se\'entli year. 
The third-year growths form a regularly ascendhig series from 7.1 inches in the oldest 
year class to 12.4 inches in the youngest, aiid the lengths of the fish at the end of their 
third year form a similar advancing .series. According to this table we should find 
that the largest series of 3-year fish in the sea at any time is com[)osed of those indi- 
viduals that will earliest mature. The same is true of the errowlh of the fourth year 



- Further Studies ou the Growth Rate in Piuific Salmon, by C. M, Frasi 
i9;o, PIT. 7-;:. Ottawa, I9?i. 



r. Conlrirjutious tu Ciuadian Biology, 1918- 



3^4 



BULLETIN OF THE BUREAU OK FISHERIES. 



and of the lifth. Slow growth and smaller size mean deferred maturity in all j-cars 
except the first and the second. 

The failure of similar results to appear in Doctor leaser's article, above referred to, 
may be due to the mixed nature of his material. His second, third, and fourth year 
classes are not composed of fish maturing in their second, third, or fourth years, but are 
accidental assemblages of fish that were in their second, third, and fourth years at the 
time they came into his hands. His second-year class doubtless contained individuals 
that would eventually mature variously in their second, third, fourth, and fifth 3'ears; 
and his third-year class, fish that would mature in their third, fourth, and fifth years. 
Under such conditions differential methods of growth of year clas,ses could not be dis- 
covered, even if they should exist. In Doctor Fraser's 1915 material it was indicated 
that the 4-year fish that were preparing to spawn were larger than those of equal age 
that would remain in the sea for another year. That result was in harmony with 
our jK-esent findings but was not verified by him in the material of 1916. 

Table 4. — CiU,cuT.ATED Growth ok Yukon King Salmon. 





Num- 
ber of 
speci- 
mens. 


Inches ii[ growth :U end of— 


Inches of grow-th during — 


Year class. 


I'irst 
year. 


Second 
year. 


Third ll'onrth 
year, 1 year. 


Fifth 
year. 


Sixth 
year. 


First 
year. 


Second 
year. 


Third 
year. 


Fourth 
year. 


F-ifth 
year. 


Sixth 
year. 


Fourth ■ 7 

Fifth it 


;. 6 

■'• 7 
3 


II. <; 
I.r6 
II 6 
II 7 


33 9 








1 


12, 4 

9 4 
76 

;. 3 




II, 7 
S. 6 
S 






, _ 






-•■ 7 
3 

•'- 5 


9 9 
S. 6 
9 2 





Sixth 

Seventh 

Average .... 


22 


ig. 2 ?7. .S 
19 ; 25 


34 


40'? 


10. 2 




67 


' 


II 9 


21 


20 5 


36 


.10. 7 2-7 


2 


9 2 


0.4 


S. 6 


6.7 



In the following table (5) is given the average weight for all specimens of a given 
length, the males and females being stated separately. The weights were taken with 
an ordinary spring-balance scales reading to poimds and half pounds. No high degree 
of accuracy can be claimed for this method, but llie results present interesting terms 
of comparison with the king salmon races of other rivers. The number of records 
available for each length is insufficient for a wholly reliable average, a fact that will 
explain irregularities in progression in the table. It will be noted that females of equal 
length with males average slightly heavier than the latter. There was no noticeable 
elongation of the jaws in the males at the time this material was examined. 

Table 5. — Average Weights by Units of Length, Yukon King Salmon, 1920. 



L'^ngth. 



16 inches, 

17 inches, 
roiuches. 
j-i inches. 
22 inches. 
-\^ inches. 
J4 inches. 
.■5 inches. 
r6 inches, 
r? inches. 
2:j inches, 
rg inches, 
.^oinches. 

31 inches. 

32 inches. 

33 inches. 



Males. 



Females. 



Number 
of speci- 
mens. 



Average Average 
weights. I weights. 



Pounds. I Pounds. 



7-8 
9.6 
10. 1 

13.6 

14 

i.j.S 
If). 4 



Kim] her 
of speci- 
mens. 



Length 



34 inches.. 

35 inches.. 

36 inches.. 
3 7inches.. 
38iiiches.. 
39inche5. . 
4otnches.. 
41 inches.. 
42inches. . 
43 inches. . 
44idches.. 
45inches. . 

46 inches.. 

47 incites.. 
4? inches.. 



Number 
of speci- 
mens. 



Average 
weights. 



Poituds. 

I8.3 

20.3 
;i. 7 

?2. 4 

25.2 
26.8 
;;9. S 
.14- 3 
36.2 
JS-9 
41. 2 
*;3- 7 



Females. 



Average 
weights. 



Pounds. 
18.3 

30-4 

22 

2.1-9 

26.3 

28 

30.5 

.14- I 

J8.3 
41-8 

42 
46.5 



Number 
of speci- 
men «:. 



14 
II 
19 



SALMON OF THE YUKON RIVEK. 



325 



The unclear area of die scales of Yukon king salmon is of extremel)' small size and 
contains correspondingly few rings. Undoubtedly this indicates comparatively very 
small size for the fmgerlings at the time of their downward migration. Our tal)lc 
indicates an average size for migrating fingerlings of 2^ inches. This is based on the 
assumption that the fry are lyi inches long when the first scale ring is formed. If, as 
seems more probable, they are slightly longer than this, our computed lengtlis of 
migrating fingerlings would be correspondingly increased but could not much exceed 
3 inches. The greatest length indicated on any scale examined by us is 4J3 inches. 
The number of nuclear rings for each vear class is as follows: 



T.Mii.r, 6. — NL.Miii;K or Nvci.f,.\r Rings, Vlkon' Kino S.m.mon, nyzo. 



ln(lividuu!s having nuclc.ir riiifis to the numlKT of- 



Fourth. , 
Filth .. 
Sixth , 
Seventh . 



6 


7 


« 


9 


10 


11 


_ 














I 





iS 


7 





I 


■I 


II 





.VI 


iS 


«; I 


10 


.-6 


i<> 


-■9 


^9 1 


7 


8 




9 


s 











Average 
, awn her 
oi rings 



K. 5 
9 I 



THE CHUM OR DOG SALMON (Oncorhynchus keta). 

The chum or dog salmon of the Yukon docs not differ from other races of chums that 
frequent streams in the more southern portion of its range either in external appearance 
or in any of the structural peculiarities that distinguish this s[)ecies. As is the case else- 
where, individuals captured in the sea or those that enter streams well in advance of the 
spawning period are symmetrical silvery fish, easily mistaken at a glance for the sockeye 
salmon. The discoloration of the skin and the elongation of the jaws, which are later 
provided with greatly enlarged teeth, are of universal occiuTcnce in this sjiccics (as, 
indeed, in all of the species of Pacific sahnon) when sexual maturity is ajiproachetl. In 
shorter streams that arc colonized by chum salmon, the fish delay entrance until nearly 
ripe and when first seen have already lost their silver}- livery. But in the Yukon, this 
species penetrates to spawning gravels in the far ui)per reaches of the river, and it pop- 
ulates as well practically all the tributaries in the middle and the lower course of the 
stream. We find, accordingly, among tlie chmns entering the mouth of the river a 
mixture of colonies, some of \vhich are bound for the headwaters, in reaching which thev 
^vill spend six weeks or more, and otliers that have not far to go. It is undoubtedly for 
this reason that the etitering fish vary so widely in different portions of the nm in the 
extent of development of those sbiking characteristics that accompany maturity. 

During the season of 1920 all the early chums were of bright silvery color and had 
abundant oil and a pinkish flesh that turned a deeper red on drying. Hut in a short 
time changes appeared, even at the mouth of the river. At first occasional individuals, 
usually males, appeared in a more advanced stage, with brightly colored bars on the sides 
of the body and with long hoolced jaws. When these were first observed they stood out 
conspicuously from their fellows, which were still in the "silver" stage. By the last of 
June these seasonal changes had become ol:)\'ious in the great mass of chums then 
nmning. It was the rule for tlie males to exliibit elongated jaws, provided with canine 
teeth, and to show the beginnings of the bright cross-bars that characterize the spawning 
males of this species. It might be thought that this dc\'elopment would continue uu- 



326 BULLETIN OF THE BUREAU OP FISHERIES. 

cliecked until the end of the season, but, strangely, during the second week in July a 
fresh run of chums that was no further advanced than were the chums of early June 
made its appearance. These also were of bright silvery color and had symmetrical 
jaws and abundant oil. Although entering relatively late, it seems safe to assume that 
this run was far from its spawning period and had far to go. Along all the lower and 
middle portions of the river fishermen who prepare dried salmon for winter use dis- 
tinguish between the silvery chums and the others. The " silvers'' have flesh of brighter 
color, rich in oil, and of more substance when dried. The others are known as "dog 
salmon," with intermediate stages called "half-breeds," and are far inferior in val-ue for 
human consumption or as dog feed. 

The Yukon chums in their prime are doubtless of far higher quality than chums 
from any other river. The differences between them and other races of chums are of 
similar nature to those that distinguish the Fraser River sockeyes from the same species 
known as red salmon in the average Alaska streams and to those that distinguish thechinook 
salmon of the Columbia from the same species ("king salmon") in the shorter streams of 
the north. The differences in all these cases are not only of similar nature, the}' are due 
to the same cause. The fine quality of Yukon chums, Fraser sockeyes, and Columbia 
chinooks is due to the great length of stream which they must traverse, while fasting, on 
the way to their spa^vning grounds and to the large store of oil that they must lay up 
for use at this time. In no other respects are the clumi salmon of the Yukon different 
from tlie same species found elsewhere. The Yukon king salmon, as we have previousl)' 
noted, are characterized by the same excessive provision of oil. They also exhibit in the 
different portions of the run equally striking differences between bright individuals, 
relatively green as to eggs and milt, and the sexually advanced forms, mth hooked 
jaws and discolored skin. It would be no less logical to recognize two or three kinds of 
king salmon than it is to distinguish, as is popularly done on the Yukon, two or three 
kinds of chums, according to the degi'ee of their advancement toward spawning. 

RATE OF TRAVEL. 

The chum salmon is generally known as a species that spawns e.Kclusively in the 
lower courses of streams, often scarcely above the reach of the tides and never far from 
salt water. It is a remarkable reversal of habit in the Yukon chums that colonies of 
them should penetrate more than 2,000 miles to the upper tributaries of that great river; 
and it testifies to the fle.\ibility of organization in salmon that a species that is in general 
not adapted to long journeys while fasting, can, under spur of necessity, make such journeys 
without food and exhibit great speed and endurance. From records of the first appear- 
ance of chums at a large number of stations during the season of 1920, it was apparent 
that their rate of travel was not far below tliat of the powerful king salmon. They 
entered the river about a week later than the kings, at Tanana they were not more than 
10 days behind the latter, and at Dawson they were some 14 days behind the kings. 
The lower 800 miles of the river, as far as Tanana, were traversed at the rate of 50 miles 
per day, and the next 700 miles, between Tanana and Dawson, were covered at the rate 
of 35 miles per day. The lower 1,500 miles were ascended at the rate of 42 miles per 
day. 

YEAR CLASSES. 

We have already noted that the king salmon of the Yukon are retarded in their 
(le\-elopment and mature on the average more than one year later than the king salmon 



SALMON Ol' THE Vl'KON KIVEK. 



from southern waters. A similar retardation is observed in chum salmon, which aver- 
age distinctly older in the Yukon than in any other region of which we have record. 

The earliest report on the ages attained by this species and on the relative propor- 
tions of the year classes was based on a small collection taken at liellingham, Wash., 
early in August, 1910.'' The number investigated was too small (58 in all) to give 
reliable averages, but the percentages indicated do not differ materially from those 
obtained in 1916 by Dr. C. M. Fraser from collections of adequate size taken at Xanaimo 
and Qualicum, in the Gulf of Georgia. In both cases the majority of the chums were 
found maturing at the age of 3 and 4 years, with very few individuals at 5 j'ears and an 
occasional rare specimen in its second year. Table 7 gives the results derived from 
both sources and also, for comparison, includes a similar groui)ing of Yukon chums. 



Tah' 



- - Vi-:ar-Ci..\ss DiSTKimTio.v. .Soi tiihkn .\.\u Vlkox Ciu'M S.M..\t!ix. 





Origin of salmon. 


: years. 


J years. 


4 years. 


5 years. 


Total. 


Southern chums: 

Rclliiigliara 


Per cent. 


0. I 


Per cent. 

53- 5 
.>4 5 


Per cent. 

44- ■< 
64- 3 
5-' 4 


Prr cent. 
I- 7 
1. 2 
■ 9 


Kitmher. 
1.300 


Qualicum 










0. I 



44. s 
3-3 


5.S- 8 
68 I 


1. t 

.•S,6 








44* 







The Yukon chums mature in their third, fourth, and fiftli years, as is the case in more 
southern waters, but the number of 5-ycar-olfls is diniinislied from nearh' half to one- 
thirtieth of the total number, and the 5-year iish show a corresponding increase from i 
to nearly 30 per cent. The retardation in the maturing of the northern race is thus 
cx'idcnt. 

PROPORTIONS OF SEXES. 

It has coninmnly been reported that dog-salmon males arc grcatlv in excess of (lie 
females, but no thoroughly satisfactory investigationof this subject has been made. To 
accomplish this, an examination would have to be made of the ratio of males to females 
at frequent intervals throughout an entire run. It might well be ex;)ccted that the 
proportions of the sexes would differ widely dining consecutive portions of the run, 
with the result that any deficiency in the number of females observed at the beginning of 
the run would be compensated for by an excess of females later on. Such an occur- 
rence lias been repeatedly observed in certain sockeye colonies. Four-year male sock- 
eyes entering Rivers Inlet, British Columbia, in 1917, varied from io<j per cent of the 
4-year class in early July to 52 per cent on July 31 ; and the 5-year males varied from 59 
])er cent of the 5-year group on July lo to 23 per cent on July 31. It is clear, therefore, 
tluit a scries of observations "ii fish hound for oric river only \\\\\ he necessarv to enable 
us to determine this point. 

Doctor Fraser's results, from fish taken partly near tlie mouth of the Little Qualicum 
River and partly from the vicinity of Nanaimo, agree in showing from both dis- 
tricts an increased percentage of males in the older year classes. The percentages of 
males in the third, fourth, and fifth year classes in the Nanaimo lot, range 42.6, 62.1, and 
loo; in the Qualicum lot, 51, 63. S, and S6.4. If these represented the average percentages 

' Age at Maturity of the Pacific Coast Salmou of the Genus Oncurhmchus. by Charies H. Gilbert. Bulletin. V. S. Bureau 
of I"isberies, Vol. XXXII. 1913 (1914), p. 18. Washington. 1913. 



328 



BULLETIN OF THE BLIREAU OF FISHERIES. 



during the entire season we should have a considerable preponderance of males over 
females on the spawning beds and we should also have indicated a relatively earlier 
maturing of females than of males. Both of these results would be unexpected. WTiilc 
no detennination has been made of the ratio of the sexes in dog-salmon fry, analogy with 
other species of salmon Avould make it appear probable that males and females are in 
approximately equal numbers at the time of hatching. If this be true, a final excess of 
males in the spawming nm could only be brought about by selective mortality directed 
against the females. It does not seem probable that this exists. As regards an earlier 
maturing of the females than of the males, producing a heavier percentage of females in 
the younger groups, ^vq can only note that this v.-ould be the reverse of what occurs in 
king salmon, sockeyes, and cohos. 

In the Bellinghara material, previ<jusly referred to, we found O7 per cent males and 33 
per cent females, the pro]X)rtion of males and females being approximately the same in 
the third and the fourth year groups. In Doctor PVaser's material, the totals showed 
59 per cent males and 41 per cent females. 

The Yukon speennens, 448 iniuunljcr, contained 57.6 percent males and 42.4 per cent 
females. The 3-ycar fish h.ad 53.3 per cent males; the 4 -year fish, 53.8 per cent; and the 
,5-year fish 67 per cent. 

3JZE AT MATURITY. 

The length and weight frequencies are given in Tables 8 and 9, which follow. These 
indicate umnistakably that tlie northern race is retarded in its growth and reaches a 
smaller size in each year class than is attained in Puget Sound and the Guh' of Georgia 
by fish of equal age. To compare with the average lengths of Yukon chums, vje repeat 
below those given by Doctor Fraser based on Qualicum and Nanaimo material. As 
measurements of the latter were taken only to tlie base of the middle caudal rays and 
our measurements include the length of the middle rays themselves, we have added 
■JJ2 per cent to Doctor Fraser's measurements to make them comparable. 

T.Miij; S. — YuKOx Chum Salmon, 1920, Grokphd uv Age. Sex, axd Lkxgth. 



Length. 



inches. . . 
inches. . . 
,S inches, 
inches.. . 
■S inches . 
inches. . , 
,5 inchc:. 
inches.. . 
.5 inches . 
inches.. . 
■S inches, 
inches.. . 
.5 inches . 
inches.. . 
.5 inches. 



Number of indiWduals in- 



Third year. 



Fe- 
males. 



Fourth year. I'ifth year 



Fe- 
males. 



I,cngth. 



Males. 


re- 
males. 






















1 

S 
4 

lO 

10 
16 
IS 


- 1 

'i' 

9 

4 ; 

5 1 

I 
I 
I 



29 inches. . . 
29.5 inches. 

30 inches. . . 
30.5 inchc?. 

31 inches.. 
31.5 inchc-. 



Number of individuals in- 



Third year. 



Fe- 
males. 



Total 


S 


Averace lenslli 




in inches 


-4 


Gulf oi Gcoriiia. 




average Icnjth 




in inches 




(Fraser) 


:S 



Fom-th year. 



164 



Fe- 
males. 



141 
24.4 



Fifth year. 



Males. 



Fe- 



86 I 



43 
JS-7 



SALMON OF THE YUKON RIVER. 
Tablk 9. — Yukon- Chum Salmon, 1920, Grouped by AgR, Sex, and \Vi:ir,nT. 



329 



W'fight. 



4 potmds . . 

5 pounds. . 

6 pounds... 

7 ixninds... 

8 pounds... 

9 pounds... 

10 pounds., 

11 pounds.. 



Number of indi\'idufds in — 



Third year. 



Fe- 
raalc-^ 



Fourth year. 



^'•>''^'- mlLJ^'-''- 



Filth year. 





J 




17 1 


7 


<;i 1 


2^ 


';^ 


5" 


' iS 


47 


2 


23 




6 





Fe- 
males.. 



Weight. 



I? pounds, 
n pounds. 
14 pounds., 
17 poiuids., 



Number of individuals in- 



Third year. 



ToUl 

Averaj;e wcichi 
in pounds 



Fe- 
males. 



Fourth year. 



164 



Fifth year. 



Fe- 
males. 



141 

f.. 5 



Fe- 
males. 



The length-weight relationship, indicated in Table 10, is given without reference 
to age. The average weight of all males and, separately, of all females that have the same 
lengtli is stated. According to this tal>le, females average shghtly lighter than males of 
equal length, those from 23 to 38 inches in lengtli averaging 97 per cent of the correspond- 
ing males. The reverse of this might have seemed reasonable because of the slightly 
lengthened jaws in tlic males. 

Tahi.e 10.- AvivKAGK Wkigiits, BY Ukits or Length, Yt kox Cmums, 1020. 



Length. 



21 inches, 
3i inches, 
3i inihes. 
T-i inches, 
2$ inches 
,•6 inches. 



Males. 


Females. i 


Speci- 
mens. 

Nutnber. 



19 

=;6 


A vcragc 
weight. 


Average 
weight. 


Speci- i 
mens. 1 


Pounds. 


P^y^^ nds. 
A 

5-1 
5-7 
6.1 
7- J 
7-9 


NunibcT. 1 

J: 




5-7 
6. 7 
7- "1 

8. -> 



Females. 



Length. 



?7 inchc 
.'8 inchc 
29 inchc 
,10 iiulir 
ji inchc 



Speci- 
mens. 



Nu'nhrr. 



Average Average 
weight. weight. 



Pounds, 
9.1 
10.3 



Spcci 
men-. 



Pounds. I Xufithcr. 

9 j : 

9-5 ■ 



GROWTH AND SCALE READINGS. 

In Figures 290 to 298 are presented photographs of a series of scales of Yukon chum 
salmon that include rei)resentatives of all the year classes found in our collection. All 
of these agree in belonging to the sea type — that is, the scales were wholly formed in 
the sea, the fry having passed out of the river at a very early age, before even the nuclear 
p'ate and the first scale ring had been formed. 

The Yukon chums agree in this respect with their souUicrn relatives. All lea\'e their 
native streams as soon as the yolk is absorbed and the)' are free swimming. In more 
southern districts this seaward migration is easily accomj^lished. The eggs are laid 
in gravels not far removed from the tides, and the young, when free, easily drop down 
with the current to the shore line. The case is less simple with the Yukon fish, many 
of which have 2,000 miles or more to cover at a period when they average only i j< inches 
long. No information is available concerning the dates on which this migration is 
effected. Observations farther south indicate a very early descent to the sea in the 
spring of the year. It is not known, however, to what extent hatching of the eggs and 
development of the young on the Yukon are retarded by the very low temperatures to 



330 BULLETIN OF THE BURH.MT OF FISHERIES. 

which they are exposed. Growth during the seaward migration can not be considerable, 
for .none of the material that we have examined indicates the formation of the scale 
nucleus while still in the stream. 

Growth of this species in the sea seems to proceed wth remarkable regularity, with 
the result that the scales are diagrammatic in their simplicity and seldom afford any 
difficulty in determination of age. In the case of the Yukon race, such uncertainty as 
may be experienced is concerned with the interpretation of the peripheral region of the 
scale and is based on the fact that the scale margins differ widely in condition among 
individuals captured on the same date. It is generally recognized that individuals of a 
given race will vary materially in the date on which they begin the rapid growth of the 
spring after the winter pause. Among the fish captured in May or early June in more 
southerly waters an occasional individual may indicate no growth of the curretit season, 
while others will vary in the number of peripheral wide rings by which the amount of 
spring growth may be computed. In the Yukon dog salmon, however, this variation 
at the time they leave their feeding grotmds and enter on their spawning run is extreme. 
.\n occasional fish, as shown by Figure 2')(', had begun no new growth of the year, the 
margin of the scale being formed by the clo.se-rmged check of the previous winter. 
Others, as represented in Figure 294, had barely inaugurated the new growth, which is 
indicated bv two or three wide rings outside the winter check. There then follow fairly 
complete series with ever-increasing growth of the season, as shown in Figm-es 297, 
290, 291, and 292, the last named having finislicd an average season's growth for the 
third year, with the exception of the winter check. 

WTien it is recalled that these dog salmon enter the Yukon in company with the 
king salmon and that the king salmon have not in any case made unmistakable growtli 
for the current season, the habit of the dog salmon in this regard seems most peculiar. 
In the early and middle parts of the run, to which alone we had access, none of the 
individuals examined had begun a winter check at tlie margin of the scales for tlie cur- 
rent )-car. Wliere a marginal winter checlc existed, it had been formed the previous 
winter and presented no real difficulty in determining age. If the latter part of the 
run should be found to contain a group of individuals in which a check was forming 
at tlie scale margin and also another group with scales like Figure 293, in which tlie 
marginal check belonged to the previous winter and no furtlier growth had been regis- 
tered, a real difficulty might arise in determining tlie age of such individuals. The 
two groups would show essentially similar scale structure, but one would be one year 
older than the other. It is not probable, however, that representatives of these two 
classes would be found together in any portion of the run. As the season advanced we 
should expect to find extremely few, if any, that had failed to produce some new 
growth of the year. 

THE SOCKEYE SALMON (Oncorhynchus nerka). 

A few scattering sockeyes (Alaska red salmon) enter the Yukon River during 
July and early August. In 1919 tlie Carlisle Packing Co. put up 22 cases of tails and 
6 cases of flats of this species and handled a total of about 300 fish. The sockeyes 
appeared even less numerous in the following year, when only 5 cases, containing about 
60 fish, were packed. 

If a permanent colony of red salmon exists in the Yukon, it must ascend to the 
lakes near the source of the river, but we have no knowledge that such spawning grounds 
for this species exist. That individuals ascend the river for long distances is certain, 



SALMON or Tun VUKOX RIVER. 331 

for we learned of their occasional occurrence up the river from men who were acquainted 
with the different species of salmon, and we obser\-ed one, a male, decidedly pink in 
color, at Ruby on August i-j, 1920, some 650 miles above the mouth of the river. 

We examined 23 specimens in 1920 on July 5, 7, 8, 9, and 13. Thirteen of tliesc 
were in tlieir fifth year (see Figs. 299 and 300), having spent their llrst year (perhaps 15 
montlis) in fresh water and having descended to the sea in their second year. The 
scales exhibit a vigorous fresh-water growth, followed by three complete year records 
at sea. A few (jf these scales, as in Figure 300, have a marginal check, which was 
formed during the preceding winter; but a majority have at the margin from one to 
four wide rings denoting new growth of the year. 

In addition to the individuals in their fifth year, one year of which was speut in 
fresh water, we have eight that had remained in fresh water an additional \car and were 
maturing in tlieir sixtli year. A scale of one of the latter class is represented in Figure 
301, the division between first and second year's growth in fresh water being clearly 
indicated. Here, again, the growth of ihe new year is faintly but unmistakablv showTi 
along the anterior left-hand margin of the scale. 

A tliird class of individuals is represented by Figure 302, thcsj having descended 
to tlie sea soon after hatching and prior to the gi-owth of tlie scale. The two salmon 
we examined belonging to the sea type, one a male 2 7>.. inches long, the other a female 
23J/2 inches long, had matured in tlieir fourth year, one year earlier th;in any of those 
that had lingered in fresh water. 

Whether the Yukon red salmon arc strays from some colony to tlie southward 
or form an unflourishing local race can not be determined at present. There is no 
reason to believe that more than one race is represented in our meager material. 

THE COHO SALMON lOncorhynchus kisutch). 

The colic or sOver salmon develops a regular run in the Yukon River, appearing 
sparingly at the mouth of the river in the latter part of July, but the run docs not show 
any real development until in August. The Carlisle Packijig Co., in 1919, packed 7 
cases of cohos on July 14 and 3 on August 2. From August 3 to 9, 59 cases were put 
up and in the following week 9S5 cases. The total pack to August 30 was 3,181 cases. 

In 1920 this species was entering the mouth of the river in very limited numbers 
during the last week in July and does not appear in the cannery puck of that year, as 
canning operations were discontinued Ijefore the run had developed. During the cailv 
half of August, between the mouth of the ri\-er and Tanana, we found at all lishing 
camps that occasional individuals were being taken. But we were unable to learn of 
its occurrence in the main river above Tanana. It is well attested that the species 
enters the Tanana and spawns in one or more tributaries of the Kantishna. How 
generally it is distributed over the basin we were unable to ascertain. 

When the coho enters the river it is a perfectly symmetrical fish, with brilliant 
silvery color, but in traversing the lower portion of the river it takes on a red livery, 
iuid the males assume at the same time the characteristic snub-nosed appearance of 
the breediiig fish, the upper jaw becoming bluntly hooked over the lower in a manner 
characteristic of this species. 

Scales of Yukon cohos are represented in Figures 2S6 to 289. As in all other coho 
colonies that we have examined, those from the Yukon are always in their second year 
(14 17°— 22 2 



332 BULLETIN OF THE BUREAU OF FISHERIES. 

of sea growth when captured,^ Outside the narrow-ringed central area, which records 
the life in fresh water, we invariably find in this species a vigorous summer growth, 
succeeded by a well-marked wijiter check, and this in turn followed by an extensive 
marginal growth of widely-spaced rings, which measure the growth of the current 
season of capture. 

In the southern part of its range, where the coho uniformly spends one season in 
fresh water before migrating seawards, the spawning run (aside from a few male grilse in 
their second year) consists exclusively of 3-year fish. As we proceed northward, how- 
ever, we encounter indi\'iduals that have tarried two years in the streams and are 
maturing in their fourth year. These are more abundant in the Yukon than in any 
other stream we have examined. Our small collection of 31 individuals comprises 12 
that have spent one year in a stream and are 3 years old (see Figs. 286 and 287) and 18 
that remained two years in fresh water and are in their fourth year (Fig. 288). If the 
customary proportions are shown in this collection, some 60 per cent of the young 
spend two years in fresh water. One individual of our collection (Fig. 289) had appar- 
ently spent three years in the river and was maturing in its fifth year. The number 
of individuals at our disposal is too small in the various classes to give reliable averages. 
Six 3-year males average 23.8 inches in length (middle caudal rays included, as in all 
our measurements) ; four 3-year females, 24.6 inches. Eleven 4-year males (two years 
in fresh water) average 24.5 inches; si.x 4-year females, 25.3 inches. As males are 
consistently larger than females among Pacific salmon, we have additional reason for 
distrusting the adequacy of the above figures. The 5-year male (three years in stream) 
is 23 inches long. 

THE HUMPBACK SALMON (Oncorhynchus gorbuscha). 

Scattering humpbacks enter the river in July and August and are then so near 
their spawning time that they would be unable to ascend the stream for any considerable 
distance. We observed one ripe male at Andreafski on August 3 and were unable to 
learn of the occurrence of the species beyond that point. 

The individuals observed were all small and without value, having often liquid 
milt and partly free eggs. Four specimens measured from 20 to 22 inches in length 
and weighed from 4 to 5 pounds. As in the case of all other humpbacks that have 
been examined for age, these were in their second year and had proceeded to sea as soon 
as free swimming, their scales registering none but .sea growth. The small size was 
doubtless due in part to the fact that they were maturing so early in the season, thus 
greatly limiting the growth of the second year. The scales all indicated this history, 
for the area representing growth of the second year was narrow and contained a partial 
check at the margin. 

* We do not here include the tew male grilse, which in more southern districts mature durina the first year at sea. 




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li'ii,;; 111 il^ ^fVi-iUli j'l-ar. 







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Fit.;, -vjo.— Scale ui chum baliuou Ldkcu Iruin iiKuUh Vukuii Rivi-r July 2, 19-0. Fciiialc. jj.'.- iiilIils Iuul', weight 

5 ix>uu(b; in its third year. 



]',ri.i.. V. S. r.. I'., u)2i-22. (Doc. 928.) 




I-'IG. .•.;!.— Sc.ik- ..i iliiiin ^almim t.ikcu (i.^n iimulh Vukmi Kivtr .liilv 

(I inniuiLi. Ill u- llurd ytur. 



o. l-Linalc. :4'.. imhcs Ion;;. nt'i':lit 



Bull. r. S. B. F., 1921-22. (Doc. >)2S.) 







Fig. 2yj.— Scale of chum s.ilniou taken frum iiioiil!! Yii!>oii River July 7, i^jo, M.ile, .3 inches long, weight 

6 puunds; in its third yL-ar. 




]'u;. 2jj. — ImjIc of cliinn bjliiion taktii (rum nioulh Yukdu River July 31, i'j:o. Mule, .^t'j iuclu-s luii.:;. wcii;lu y 

puuiuh; iu iu lourth year. 



Bull. U. S. IJ. I'., i')2i-22. (Due. n:S.) 




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Fig. :'m- — ^^calc of Lhuiu ^ahuun lakcii from niuuth Yukon Ki\ cr July 7, I'^.'o. Kcmalc, 23 iuchfb loup, ^vvi^;ht 

5 pounds; in its fourth year. 



ll'LL- U. S. r>. 1'., lO-I---. { I^"C. 0^!^^ ) 




I'ir. :j5. — SluK- nf fhum salni.iii l,iki.n in. in niniih \'ukMii ki\.i luK ii. i^^i. Male, j;',- irRlR> !oii.;, wcj^li 

') iiuuiiii^, ill its (((urlli scar 



BUI.L. U. vS. P>. I-., 1921-22. (Doc. 928.) 




Fig. .'96.— Scale o[ lIiuui -.alniuu Uiktii In m iiuiuili \ vikon Kivcr July 2. ig-'o. Female, ib mcUcb long, weight 

7 pounds; in it^ fifih year. 



Hull. U. S. P.. I'., ic)2r-22. fDoc. 02.S.) 




Fig. 2<-)-. — Suit- of clunii ^.lllllnll uiLtii limii iii-inih \ukiiii |-;i\ir JiiK- 7. igjo. iVinak', .-.i', nu lu-. luu^. weii:lit 

7 [»oiuid\; in its liiiU ytar. 



bt'tx- r. s. r>. F., 1921-22. (1)00.028.) 




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10 puimd^". in it? liflh >'car. 






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